Canon D646U - Manual (Page 54)

54
S T E P 3
Scanning Techniques
Matching Scan Resolution to Purpose
Plug-in Module CS-U provides many choices of resolution. The resolution you
choose should depend upon your output device, the intended purpose of the
image, the type of image and your scanner.
It is generally recommended that you scan at a higher resolution than required for
output. This ensures that you obtain the best quality image, which can then be
reduced with an image editing program to suit specific purposes.
Different types of images require different scan settings. However, increases in scan
resolution have a diminishing return after a certain point. For example, a text
image can be scanned at 600 dpi for output to a 600 dpi laser printer, while a color
image should be scanned at 180 dpi to be output to a color bubble jet printer (360
dpi). To output a color or grayscale image to a bubble jet printer, use a resolution
equal to half the resolution of the printer. Set the resolution to 180 dpi, for
example, for output on a 360 dpi printer.
• Scan in black and white mode if you are scanning line art or other items that are
black and white with no shades of gray.
• Scan in black and white mode if you are scanning a text image for conversion to
editable text.
• Scan in grayscale mode if you are scanning continuous-tone black and white
photographs, charcoal drawings or originals with shades of gray.
• Scan in Color mode if you are scanning full-color images, such as photographs or
illustrations.
• If you are using an OCR (optical character reader) program in black and white
mode, you are recommended to select a resolution higher than 300 dpi.
• The minimum scannable height and width will vary with the scanning resolution.
At 75 dpi, for example, the minimum selectable height and width in the preview
area is 9 pixels (approximately 0.12 inches or 0.30 cm). At 300 dpi, it is 35 pixels
(approximately 0.12 inches or 0.30 cm).
Optical Resolution
Optical resolution refers to the amount of information a scanner can sample per
inch. Different varieties of scanner feature different optical resolutions. The
maximum optical resolution of the CanoScan D646U models is 600 dpi for the
primary scan (horizontal dimension of the document), and 1200 dpi for the
secondary scan (vertical dimension).